I've been trying to find this through search but not having any luck. I'm not good at wiring don't really like it much. However I have a 2004 Golf and the passenger side bright headlight isn't working. With a bit of checking I found that I'm only getting 7 volts to the headlight from the harness. All other lights are working. I looked as best I could in the Bentley but I have no skill with these diagrams. I suspect that both lights somehow feed together but was wondering if someone can point me in the right direction as to where a problem might exist. It does have Hella Glass front fixtures and HID low beams installed, however that all works its just the Bright light. Any help would be appreciated.
Low voltage to headlight
- Thread starter TNTKNC
- Start date
BobnOH
not-a-mechanic
What did the other lights measure? Since I don't know if 7 V isn't correct, if that's way low it's more than likely a wire or connector.
First off I’m assuming you checked the bulb 
I would plug the bulb back into the socket and with the light switch ON perform a voltage drop test on that circuit
To keep the math easy and less confusing your going to perform two tests on the circuit.
1) With the voltmeter set at 20v take one lead of your dvom and back probe the negative wire on the light socket and the other lead connect it to the negative battery post. Record your reading
2) perform the same test, as above, but do the positive side of the circuit. Record your reading
Note: in order for the above test to be valid you MUST have the bulb(load)plugged in and the lights ON. In both tests you don’t won’t to see a voltage reading greater than 0.5 V. If you do, then you have an issue with the circuit ( corrosion, bad connection etc)
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I would plug the bulb back into the socket and with the light switch ON perform a voltage drop test on that circuit
To keep the math easy and less confusing your going to perform two tests on the circuit.
1) With the voltmeter set at 20v take one lead of your dvom and back probe the negative wire on the light socket and the other lead connect it to the negative battery post. Record your reading
2) perform the same test, as above, but do the positive side of the circuit. Record your reading
Note: in order for the above test to be valid you MUST have the bulb(load)plugged in and the lights ON. In both tests you don’t won’t to see a voltage reading greater than 0.5 V. If you do, then you have an issue with the circuit ( corrosion, bad connection etc)
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Mongler98
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Use a volt meter or a prob and test the voltage at the fuse for both headlights. If you have 12 at both, your issue probably is within the relay for the high low beam. Find the relay and test it.
i would put my money on a bad relay. they do after all just have contacts in them and with age, they start to get pitted from arcing.
i would put my money on a bad relay. they do after all just have contacts in them and with age, they start to get pitted from arcing.
[QUOTE=mr.loops;
1) With the voltmeter set at 20v take one lead of your dvom and back probe the negative wire on the light socket and the other lead connect it to the negative battery post. Record your reading
2) perform the same test, as above, but do the positive side of the circuit. Record your reading
Note: in order for the above test to be valid you MUST have the bulb(load)plugged in and the lights ON. In both tests you don’t won’t to see a voltage reading greater than 0.5 V. If you do, then you have an issue with the circuit ( corrosion, bad connection etc)
This is exactly how you do this, however if the headlight bulb is a high and low beam in one you can skip the voltage drop test on the ground side as the low beam works and uses the same ground as the high side.
The wire you want to check is the power wire for the high beam the one he says he has 7 volts on, from the bulb to the battery. Not doubt there will be a drop that is to high. From there you move the probe closer to the battery from the bulb until voltage is low, less than .5 volt. In most cases you like to see .2 to .3 volt. In this circuit higher would likely not be noticed.
1) With the voltmeter set at 20v take one lead of your dvom and back probe the negative wire on the light socket and the other lead connect it to the negative battery post. Record your reading
2) perform the same test, as above, but do the positive side of the circuit. Record your reading
Note: in order for the above test to be valid you MUST have the bulb(load)plugged in and the lights ON. In both tests you don’t won’t to see a voltage reading greater than 0.5 V. If you do, then you have an issue with the circuit ( corrosion, bad connection etc)
This is exactly how you do this, however if the headlight bulb is a high and low beam in one you can skip the voltage drop test on the ground side as the low beam works and uses the same ground as the high side.
The wire you want to check is the power wire for the high beam the one he says he has 7 volts on, from the bulb to the battery. Not doubt there will be a drop that is to high. From there you move the probe closer to the battery from the bulb until voltage is low, less than .5 volt. In most cases you like to see .2 to .3 volt. In this circuit higher would likely not be noticed.